Forum: Virtual Classroom - Antenna

Antenna

Okay I thought It would be nice to see how everyone is building there antenna's, So we can share with others and maybe come up with a better antenna for all, So please lets see some pictures and building instructions. Also show your tracking system mechanics.
Thanks SamSam5th Feb 201613:59

Sorry about the Antenna spelling guess i was to fast for the computer 8)
Sam5th Feb 201614:00

Fantastic idea Sam, and one of the key reasons we built this section.

At the moment, we don't have a way to load photos to the forum, but using a service like www.imgur.com or something similar and posting a link would work well. Imgur is very simple to use, no account creation is required and you can simply upload your photo to that site and then post the link here.

I'll go first.

http://imgur.com/yrcyZtH

Is a YAGI I made for 435Mhz using a piece of aluminum U channel with 6AWG copper ground wire and Nylon inserts to isolate the elements from the boom.

It was the first one I ever made and I kept it on the wall until very recently, just for nostalgia purposes.

Now I challenge everyone else to post theirs! :-)

Wade
Wade5th Feb 201618:49

I made a 440 mhz antenna with a peace of 1x1 wood and coat hanger wire. The copy of the Arrow antenna. Worked great with the cube sats.

John
John6th Feb 201622:03

It would be great to see photos John.

I'm also very curious how did you connect the coax cable conductor and shield to the coat hanger wire??

Wade

Wade7th Feb 201617:42

Well the exact wire that I used was the steel u shaped wire that a lot of temporary signs use. I use to see all of the u wire at the stop signs waiting for the lawn mower to hit so I picked it up. Since I was using 2m and 440 this was the wire I used. For 440 i will just use steel coat hanger wire. It is steel and can be soldered with a little heat. The coax that I used was RG-58 witch is copper. i have seen different crimp/clamp arrangements used with the aluminum coax that I will have to find again.
John
John7th Feb 201618:13

The Controlled Impedance "Cheap" Antennas directions show a simple design. Are the shapes of these types of antennas really that simple? What I've researched so far shows a design like one would see on the roof of a house. Has anyone found a resource with multiple design options or explanations of vocabulary?

Brock

P.S. Cheryl VanLandingham mentioned the ThumbSats transmit a frequency of 401.5 MHz. John, does your 440 MHz antenna capture a wide range of frequencies? I have literally know practical/applicable knowledge of antennas so I'm quite unsure of what to do.
Brock24th Feb 201622:33

Brock,

You are correct, ThumbSat is to transmit at 401.5MHz.

Someone MUCH more knowledgeable than I should comment, but in the simplest terms, almost all the variables in an antenna affect sensitivity to specific frequencies. The length and diameter as well as the spacing of each element all affect the tuned frequency.

Obviously, the closer to the specific frequency you can get, the higher the gain will be for that frequency and the better results you will have.

How far away the frequency of an antenna can be tuned and still be good for effectively receiving 401.5MHZ, I have not tested. Maybe John can comment when he has time.

Wade

Wade26th Feb 201622:46

Since we are talking about home-made antennas without the benefit of antenna analyzers, I suspect that most of our antennas will not be very accurate compared to a high quality factory antenna. Not accurate in resonate frequency, nor in gain, nor impedance.

But, if the antenna resonant frequency is 40 Mhz from 401.5 Mhz, then there will be a problem with gain. Actually, a single dipole antenna resonant at the right freq will probably work better..

A yagi beam antenna consist of three major parts, the most important is the driven element which has the coax/feed-line connected. To work properly, this element must be resonant at the operating frequency. A standard yagi beam's driven element is a resonant 1/2 wavelength of the operating frequency. It can be other lengths, but the impedance will change and a UNUN is required to match the feed-line.

The next most important part of the yagi is the directing elements, which are slightly shorter than the driven element and are spaced according to the resonant frequency of the driven element. This spacing is critical..

The third part of the yagi is a reflector element, which is slightly longer than the driven element and is placed at the back of the beam. The length and spacing is critical to the operating frequency..

But, with careful attention to the build of the yagi, satisfactory results can be achieved. Usually within 3db of a commercial beam, especially if the yagi is five elements or less..

Good electrical connection from the feed-line to the driven element is critical as is the quality of the feed-line. Even with short lengths of feed-line, proper impedance and shielding are very important.

Also, when cutting the lengths of wire for the elements, use the material specified if possible as different conductors have a different 'electrical length'. Of course, if we have access to the electrical characteristics of each type of wire/conductor, then we can calculate the difference in length of each element and the spacing between them.
Bobbie6th Mar 201600:05